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Editing: frames.py
from __future__ import annotations import dataclasses import enum import io import secrets import struct from typing import Callable, Generator, Optional, Sequence, Tuple from . import exceptions, extensions from .typing import Data try: from .speedups import apply_mask except ImportError: # pragma: no cover from .utils import apply_mask __all__ = [ "Opcode", "OP_CONT", "OP_TEXT", "OP_BINARY", "OP_CLOSE", "OP_PING", "OP_PONG", "DATA_OPCODES", "CTRL_OPCODES", "Frame", "prepare_data", "prepare_ctrl", "Close", ] class Opcode(enum.IntEnum): """Opcode values for WebSocket frames.""" CONT, TEXT, BINARY = 0x00, 0x01, 0x02 CLOSE, PING, PONG = 0x08, 0x09, 0x0A OP_CONT = Opcode.CONT OP_TEXT = Opcode.TEXT OP_BINARY = Opcode.BINARY OP_CLOSE = Opcode.CLOSE OP_PING = Opcode.PING OP_PONG = Opcode.PONG DATA_OPCODES = OP_CONT, OP_TEXT, OP_BINARY CTRL_OPCODES = OP_CLOSE, OP_PING, OP_PONG # See https://www.iana.org/assignments/websocket/websocket.xhtml CLOSE_CODES = { 1000: "OK", 1001: "going away", 1002: "protocol error", 1003: "unsupported type", # 1004 is reserved 1005: "no status code [internal]", 1006: "connection closed abnormally [internal]", 1007: "invalid data", 1008: "policy violation", 1009: "message too big", 1010: "extension required", 1011: "unexpected error", 1012: "service restart", 1013: "try again later", 1014: "bad gateway", 1015: "TLS failure [internal]", } # Close code that are allowed in a close frame. # Using a set optimizes `code in EXTERNAL_CLOSE_CODES`. EXTERNAL_CLOSE_CODES = { 1000, 1001, 1002, 1003, 1007, 1008, 1009, 1010, 1011, 1012, 1013, 1014, } OK_CLOSE_CODES = {1000, 1001} BytesLike = bytes, bytearray, memoryview @dataclasses.dataclass class Frame: """ WebSocket frame. Attributes: opcode: Opcode. data: Payload data. fin: FIN bit. rsv1: RSV1 bit. rsv2: RSV2 bit. rsv3: RSV3 bit. Only these fields are needed. The MASK bit, payload length and masking-key are handled on the fly when parsing and serializing frames. """ opcode: Opcode data: bytes fin: bool = True rsv1: bool = False rsv2: bool = False rsv3: bool = False def __str__(self) -> str: """ Return a human-readable represention of a frame. """ coding = None length = f"{len(self.data)} byte{'' if len(self.data) == 1 else 's'}" non_final = "" if self.fin else "continued" if self.opcode is OP_TEXT: # Decoding only the beginning and the end is needlessly hard. # Decode the entire payload then elide later if necessary. data = repr(self.data.decode()) elif self.opcode is OP_BINARY: # We'll show at most the first 16 bytes and the last 8 bytes. # Encode just what we need, plus two dummy bytes to elide later. binary = self.data if len(binary) > 25: binary = b"".join([binary[:16], b"\x00\x00", binary[-8:]]) data = " ".join(f"{byte:02x}" for byte in binary) elif self.opcode is OP_CLOSE: data = str(Close.parse(self.data)) elif self.data: # We don't know if a Continuation frame contains text or binary. # Ping and Pong frames could contain UTF-8. # Attempt to decode as UTF-8 and display it as text; fallback to # binary. If self.data is a memoryview, it has no decode() method, # which raises AttributeError. try: data = repr(self.data.decode()) coding = "text" except (UnicodeDecodeError, AttributeError): binary = self.data if len(binary) > 25: binary = b"".join([binary[:16], b"\x00\x00", binary[-8:]]) data = " ".join(f"{byte:02x}" for byte in binary) coding = "binary" else: data = "''" if len(data) > 75: data = data[:48] + "..." + data[-24:] metadata = ", ".join(filter(None, [coding, length, non_final])) return f"{self.opcode.name} {data} [{metadata}]" @classmethod def parse( cls, read_exact: Callable[[int], Generator[None, None, bytes]], *, mask: bool, max_size: Optional[int] = None, extensions: Optional[Sequence[extensions.Extension]] = None, ) -> Generator[None, None, Frame]: """ Parse a WebSocket frame. This is a generator-based coroutine. Args: read_exact: generator-based coroutine that reads the requested bytes or raises an exception if there isn't enough data. mask: whether the frame should be masked i.e. whether the read happens on the server side. max_size: maximum payload size in bytes. extensions: list of extensions, applied in reverse order. Raises: EOFError: if the connection is closed without a full WebSocket frame. UnicodeDecodeError: if the frame contains invalid UTF-8. PayloadTooBig: if the frame's payload size exceeds ``max_size``. ProtocolError: if the frame contains incorrect values. """ # Read the header. data = yield from read_exact(2) head1, head2 = struct.unpack("!BB", data) # While not Pythonic, this is marginally faster than calling bool(). fin = True if head1 & 0b10000000 else False rsv1 = True if head1 & 0b01000000 else False rsv2 = True if head1 & 0b00100000 else False rsv3 = True if head1 & 0b00010000 else False try: opcode = Opcode(head1 & 0b00001111) except ValueError as exc: raise exceptions.ProtocolError("invalid opcode") from exc if (True if head2 & 0b10000000 else False) != mask: raise exceptions.ProtocolError("incorrect masking") length = head2 & 0b01111111 if length == 126: data = yield from read_exact(2) (length,) = struct.unpack("!H", data) elif length == 127: data = yield from read_exact(8) (length,) = struct.unpack("!Q", data) if max_size is not None and length > max_size: raise exceptions.PayloadTooBig( f"over size limit ({length} > {max_size} bytes)" ) if mask: mask_bytes = yield from read_exact(4) # Read the data. data = yield from read_exact(length) if mask: data = apply_mask(data, mask_bytes) frame = cls(opcode, data, fin, rsv1, rsv2, rsv3) if extensions is None: extensions = [] for extension in reversed(extensions): frame = extension.decode(frame, max_size=max_size) frame.check() return frame def serialize( self, *, mask: bool, extensions: Optional[Sequence[extensions.Extension]] = None, ) -> bytes: """ Serialize a WebSocket frame. Args: mask: whether the frame should be masked i.e. whether the write happens on the client side. extensions: list of extensions, applied in order. Raises: ProtocolError: if the frame contains incorrect values. """ self.check() if extensions is None: extensions = [] for extension in extensions: self = extension.encode(self) output = io.BytesIO() # Prepare the header. head1 = ( (0b10000000 if self.fin else 0) | (0b01000000 if self.rsv1 else 0) | (0b00100000 if self.rsv2 else 0) | (0b00010000 if self.rsv3 else 0) | self.opcode ) head2 = 0b10000000 if mask else 0 length = len(self.data) if length < 126: output.write(struct.pack("!BB", head1, head2 | length)) elif length < 65536: output.write(struct.pack("!BBH", head1, head2 | 126, length)) else: output.write(struct.pack("!BBQ", head1, head2 | 127, length)) if mask: mask_bytes = secrets.token_bytes(4) output.write(mask_bytes) # Prepare the data. if mask: data = apply_mask(self.data, mask_bytes) else: data = self.data output.write(data) return output.getvalue() def check(self) -> None: """ Check that reserved bits and opcode have acceptable values. Raises: ProtocolError: if a reserved bit or the opcode is invalid. """ if self.rsv1 or self.rsv2 or self.rsv3: raise exceptions.ProtocolError("reserved bits must be 0") if self.opcode in CTRL_OPCODES: if len(self.data) > 125: raise exceptions.ProtocolError("control frame too long") if not self.fin: raise exceptions.ProtocolError("fragmented control frame") def prepare_data(data: Data) -> Tuple[int, bytes]: """ Convert a string or byte-like object to an opcode and a bytes-like object. This function is designed for data frames. If ``data`` is a :class:`str`, return ``OP_TEXT`` and a :class:`bytes` object encoding ``data`` in UTF-8. If ``data`` is a bytes-like object, return ``OP_BINARY`` and a bytes-like object. Raises: TypeError: if ``data`` doesn't have a supported type. """ if isinstance(data, str): return OP_TEXT, data.encode("utf-8") elif isinstance(data, BytesLike): return OP_BINARY, data else: raise TypeError("data must be str or bytes-like") def prepare_ctrl(data: Data) -> bytes: """ Convert a string or byte-like object to bytes. This function is designed for ping and pong frames. If ``data`` is a :class:`str`, return a :class:`bytes` object encoding ``data`` in UTF-8. If ``data`` is a bytes-like object, return a :class:`bytes` object. Raises: TypeError: if ``data`` doesn't have a supported type. """ if isinstance(data, str): return data.encode("utf-8") elif isinstance(data, BytesLike): return bytes(data) else: raise TypeError("data must be str or bytes-like") @dataclasses.dataclass class Close: """ Code and reason for WebSocket close frames. Attributes: code: Close code. reason: Close reason. """ code: int reason: str def __str__(self) -> str: """ Return a human-readable represention of a close code and reason. """ if 3000 <= self.code < 4000: explanation = "registered" elif 4000 <= self.code < 5000: explanation = "private use" else: explanation = CLOSE_CODES.get(self.code, "unknown") result = f"{self.code} ({explanation})" if self.reason: result = f"{result} {self.reason}" return result @classmethod def parse(cls, data: bytes) -> Close: """ Parse the payload of a close frame. Args: data: payload of the close frame. Raises: ProtocolError: if data is ill-formed. UnicodeDecodeError: if the reason isn't valid UTF-8. """ if len(data) >= 2: (code,) = struct.unpack("!H", data[:2]) reason = data[2:].decode("utf-8") close = cls(code, reason) close.check() return close elif len(data) == 0: return cls(1005, "") else: raise exceptions.ProtocolError("close frame too short") def serialize(self) -> bytes: """ Serialize the payload of a close frame. """ self.check() return struct.pack("!H", self.code) + self.reason.encode("utf-8") def check(self) -> None: """ Check that the close code has a valid value for a close frame. Raises: ProtocolError: if the close code is invalid. """ if not (self.code in EXTERNAL_CLOSE_CODES or 3000 <= self.code < 5000): raise exceptions.ProtocolError("invalid status code")
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